On Ubuntu Server 12.04, how can I configure an account to use a locale other than the system default local? Say if I wanted Russian users to be able to use Russian in the terminal ... and Polish users to use Polish, how can I achieve that?

The default locale is supposed to remain at en_US in its various incarnations (it defaults to the UTF-8 variant).

The ideal solution would be something where I can set it in adduser and friends, but I didn't find such option.